The present inventions are related to systems and methods for transferring information, and more particularly to systems and methods for transferring information from a storage medium.
In a traditional storage device, information is longitudinally recorded on a magnetic storage medium. In a longitudinal recording scenario, data detection processes key on data transitions. As such, low frequency components (including any DC component) of the signal sensed from the magnetic storage medium do not convey information and may be eliminated. In addition, there is a desire to provide a high pass filter in a preamplifier associated with a data detection system to allow for fast write to read recovery.
In contrast to longitudinal recording where data detection keys on transitions, in newer perpendicular recording approaches the magnitude of the field sensed from the magnetic storage medium carries information. In such a case, use of a high pass filter in the preamplifier likely eliminates some information sensed from the magnetic storage medium. As disk format efficiency demands low coding overhead, the capability to provide for detecting low frequency components by means of RLL encoding is limited. In some cases, the aforementioned loss of low frequency energy has resulted in a higher bit error rate in devices using perpendicular recording approaches.
Some prior art data detection systems seek to reduce the loss of lower frequency information through use of a feedback loop. FIG. 1a depicts such a prior art data detection system 101. Data detection system 101 receives an analog input signal 106 that was previously high pass filtered by a preamplifier resulting in the removal of some low frequency information. An analog to digital converter 121 receives analog input 106 and provides a series of digital samples 126 that are provided to a finite impulse response equalizer 131. Equalizer 131 provides a filtered output 136 to a summation element 138, and the output of summation element 138 is provided to a Viterbi algorithm detector 151 which provides a detected output 196. Detected output 196 is fed back through a baseline feedback compensation circuit 171 that provides an output which is aggregated with filtered output 136 using summation element 138. In operation, baseline feedback compensation circuit 171 (e.g., a low frequency filter) provides for correction of low frequency information lost during high pass filtering. The latency of the feedback loop including Viterbi algorithm detector 151 and baseline feedback compensation circuit 171 can be significant. This latency reduces the effectiveness of any attempt to recover the lower frequency information and results in an increased bit error rate for a given input data set.
To reduce the effect of latency, some prior art data detection systems include the use of both feed forward and feedback compensation to restore some of the lower frequency information eliminated by the high pass filter. FIG. 1b depicts such a prior art data detection system 100. Data detection system 100 receives an analog input signal 105 that was previously high pass filtered by a preamplifier resulting in the removal of some low frequency information. An analog to digital converter 120 receives analog input 105 and provides a series of digital samples 125 that are provided to a finite impulse response equalizer 130. Equalizer 130 provides a filtered output 135 to a baseline feed forward compensation circuit 180. An output of baseline feed forward compensation circuit 180 is aggregated with filtered output 135 using a summation element 137. The output of summation element 137 is provided to a Viterbi algorithm detector 150 which provides a detected output 195. Detected output 195 is fed back through a baseline feedback compensation circuit 170 that provides an output which is also aggregated using summation element 137. In operation, baseline feedback compensation circuit 170 provides for correction of low frequency information lost during high pass filtering. The latency of the feedback loop including Viterbi algorithm detector 150 and baseline feedback compensation circuit 170 can be significant. To reduce the effect of such latency, baseline feed forward compensation circuit 180 provides an inverse high pass filter tuned to compensate for the upstream high pass filter removing low frequency information. This results in a non-latent attempt at low frequency information recovery that is used in addition to that provided by baseline feedback compensation circuit 170. Such an approach of using both feed forward and feedback compensation circuits provides reasonable performance, however, the feed forward compensation offers limited capability and can be very noisy.
Hence, for at least the aforementioned reasons, there exists a need in the art for advanced systems and methods for accessing information from a storage medium.